Recent studies of memory phenomena in animals indicate the importance of retrieval deficits as sources of retention loss. The proposed research focuses on manipulations which modulate memory in an attempt to elucidate further the nature of retrieval processes. One series of studies examines the way in which types of stimuli effective in reactivating old memory interact with the age of the information being retrieved. Changes in effectiveness of reactivation will be assessed in terms of vulnerability of memory to disruption by amnestic and counterconditioning treatments. Other work will continue to explore the phenomenon of memory "counterconditioning" with particular emphasis on determining whether this effect represents a form of competing learning, altered retrieval, or integration of new information (malleability). Investigation of certain aspects of anterograde amnesia, and the relationship between anterograde and retrograde memory loss, will also be undertaken.